Crystal holder



E. F. KIERNAN Feb. 7, 1950 CRYSTAL HOLDER Filed Feb. 24, 1949 D v n 3 H w vl 9 w A w EG.Z.

INVENTOR.

EARL E K/E/PNAN ATTORNEY Patented Feb. 7, 1950 CRYSTAL HOLDER Earl F. Kiel-nan, San Diego, Calif.

Application February 24, 1949, Serial No. 78,203

6 Claims.

(Granted under the act of MarchS, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates to crystal assemblies and, more particularly, to such assemblies wherein the crystal forms a part of the holder or casing, with one surface of the crystal exposed for contact by the external medium surrounding the assembly.

It is an object of this invention to provide a crystal assembly in which a maximum area of the crystal is employed to transfer energy between the electrodes on each face of the crystal and the ambient medium adjacent the crystal holder.

It is another object of this invention to in crease the power transfer capacity of a crystal holder assembly.

It is a further object of this invention to provide a sonic transducer in which a large portion of the crystal face is directly in contact with the sonic transmitting medium.

It is another object of this invention to provide insulating means of increased effectiveness at the edge of a transducer crystal, thereby to prevent electrical breakdown around the edge of the crystal between two electrodes mounted on the respective faces of the crystal.

'Other objects and. many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to thefollowing description.

In accordance with the instant invention, the crystal assembly comprises a casing,-at least one face of which is open. Across this opening and sealed to the edge thereof is mounted a plate-like crystal, which serves to close the opening and to seal the casing. Thin, conducting, plate-like electrodes are mounted, one on each face of the crystal.

When used to transfer energy from an electrical state to a physical or sonic state, it is often requisite that the electrodes haveapplied thereto a considerable potential. A major problem is thus one of insulating the two electrodes from each other so that the potential does not form an arc around the edge of the crystal between the edges of the two electrodes. To guard against this difiiculty, there is provided, in accordance with the instant invention, a sealed chamber which is bordered, at least in part, by an annulus adjacent the edge of the electrode on the inner face of the crystal, this annulus lying across the breakdown path between the two electrodes, so that by providing the chamber with a medium of good insulating properties, the breakdown resistance across the annular path may be made high, thereby preventing electrical breakdown between the electrodes. This insulation may be effected by contacting the annular face around the crystal with an insulating fluid such as oil, or by providing a vacuum adjacent the face, either of which expedients results in high breakdown resistance across the annulus.

A pair of conductors are provided in contact with each of the respective electrodes, and termi nate in appropriate terminals to which a suitable electric circuit may be attached.

Two specific embodiments of the invention described generally above will now be illustrated in connection with the accompanying drawings, wherein:

Fig. 1 is a perspective, partially sectioned view of a first embodiment of the instant invention; and

Fig. 2 is a similar view of a second embodiment of the instant invention.

Referring to Fig. 1, the crystal assembly is shown comprised of a pair of cylinders I I and I2, made of insulating material and disposed one within the other, thereby forming between them an annular chamber I3. A round, disk-like crystal I is mounted across the bottom end I6 of the inner cylinder I I and sealed to the bottom edge of the cylinder. The crystal I4 is anX-cut, quartz crystal which vibrates longitudinally, that is, in its thickness, so that when an electric field is applied across the thickness of the crystal, a corresponding physical vibration occurs also across the thickness of the crystal.

As shown in Fig. 1, the diameter "of the crystal I4 is slightly larger than that of the inner cylinder I I, so that the periphery of the crystal I4 extends slightly beyond the edge of the inner cylinder and terminates in an edge H. An annular wall I8 is mounted across the bottom edge of the outer cylinder I2 and is provided with a circular groove I9, into which fits the bottom edge of the cylinder I 2, thereby simplifying sealing of the edge of the cylinder I2 to the annular wall I8. The inner edge 2| of the annular wall I8 is sealed to the edge 51 of the crystal I4, thereby sealing the bottom end of the annular chamber I3. The annular wall I8 is of greater diameter than is the outer cylinder I2, so that it continues beyond the edge of the outer cylinder I2 and forms a circumferential flange 22 therearound.

Another wall 23 is provided at the upper end of the two cylinders II and I2, and is made in the form of a cap having internal threads 24 so that it may be screwed onto corresponding thread 26 on the upper end of the outer cylinder I2, thereby to closethe upper end of the crystal assembly. A I

3 disk-like washer 21 is positioned between the wall or cap 23 and the upper edges of the cylinders H and I2, so that as the cap 23 is screwed on ti htly, these edges are sealed to the cap, thereby sealing the upper end of the annular chamber I3, which is filled with a suitable insulating medium such as oil 28. V

A pair ofthin, iplate-like electrodes 3] and 32 are mounted one against each face of the crystal l4. These electrodes preferably consist of thin films of silver and copper evaporated or sputtered onto the two faces of the crystal [4. A terminal 33 is mounted in the flange 22 of the walllt, and a resilient conductor 34 is secured at one end to the terminal 33, the inner end 36 of the conductor being pressed against the outer electrode: 32 to make 'good electrical contact therewith. Another terminal 3'! is mounted in and extends thru the upper wall 23. A conductor 38 extends between the terminal 3's and the electrode 3| 5011 the inner face of the crystal; theinner, resilient end 39 of this conductor also making electrical contact by pressing against the electrode.

Typical use of the assembly illustrated in Fig. 1 is for the purpose-oi transdu'cing electrical vihrations applied to the terminals 33 and 37 into sonic vibrations emanating from thickness vibrations of the crystal l t. Insn'any cases, to achievesatis factory transmission, it is necessary to apply high potential difference between the two electrodes 3] and'32. A major problem encountered with the use of such potentials is'the danger of voltage breakdown between the edges of the electrodes 3! and 32 around the edge I! of the crystal I'll This danger is obviated in the instant invention by providing that a closed annulus 4! at the edge of the crystal M is in contact with the oil 28 in the chamber'lt, the oil constituting a good insulator to prevent arcing around the edge of the crystal. Substantially 'thesame insulating results could be achieved by eliminating the inner cylindo H, and filling the entire space back of the crystal M with oil. This would carry the disadvantage-of robbing'the crystal assembly of much of its transduced sonic energy, which would be absonbed by the oil'conta'cting the inner face of the crystal it. By removing the oil from the center portion ofthe crystal, and allowing the oil to fillonly a small annulus at the edgethe power transmitted is substantially doubled, since vir-,

tuallyall of the power is then able to bidelivered to the outer face (lithe-crystal i l. r

Another embodiment of the instant invention,

shown Fig; 2, comprises a hollow casing 51hr insulating material and having an opening 52 in is lower face thereof. A plate crystal 53 is mountedacross the opening, the edge of the crystal 53 beingsealed tothe edge of an inwardly ex tending flange 54, forming the border-of the opening 52. A thin electrode 56 is mounted against the inner face of the crystal 53, the edge 57 of the electrode 55 terminating short of the opening 55'inthecasing 5 5, thereby leaving an annulus 58 of bare crystal exposed to the interior of the cas ing'si. An outer electrode 59 is mounted against the outer face of the crystal '53. A resilient cod-- ductcr Bil extends betweenthe outer electrode 59 and an exteriorterminal5i mounted tothe easing 55. A terminal t t-penetratesthe upper wall of the casing 5%, the. penetration of the wall being sealed as shown at'63 arund'the terminal 52; A resilient conductor 64 extends between the inner end or the terminal 62 and the electrode 55 onthe'inneriace'of the crystal 53.

The'entire casing 51 is evacuated so that an name annulus of insulation at 58 is provided between the two electrodes 56 and 59, thereby preventing arcing between the two electrodes around the edge of the crystal 53, in a manner similar to that described in connection [with the first embodiment.

For the sake of clarity, the crystal and electrodes 'il l ustrated in the drawing have been shown of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise I than as specifically described.

, The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or-therefor. Y i

' Vl'fhat is claimedis: 1

1. A- crystal assembl comprising :a pair of cyl inders', onew'ith'in the'cther-,-iorining an annular chamber between, a plate crystal mounted across one end-of the inner cylinder and sealedto the edge thereof the peripherycf said crystal extend ing slightlybeyond the edge'ofisaid inner cylin der, -an annular wall-sealed 'to the-edge-oT Said "outer cylinder and to the edge of said crystal thereby to seal said chamber at said one end,-said annular walicontinuin' beyond the edge or said outer-\cylinder-to rorin a'circumierential flange, a Wall at'the other end of said assembly sealed te the cylinder e'dfgesto seal 1 said chamber, aminsulati'ng fluid filling said chamber, a pair 'of thin; plate-like eie'ctrodesmounted one against eat/1 1 face of said crystal, at first terminal-mounted to said fiance, a conductor extending between said first ternnnal and the electrode onthe outer race or said crystal, a second terminal mountedto said second named wall, anda conductor extending be= tween said second terminal and the electrode on the inner face of said crystal.

2. Acrystal assemblycomprising a pair" of cylinders, onew-ith-in the other, forming an annular chamber between; a-plate crystal mounted across one end of the inner'cylinder and "sealed to the edge thereof; an annular wall sealed to the edge of said outer cylinder and to the edge of said crystal and sealing said chamber at said one end, said annular wall'continuing beyond the edge of said outer cylinder to form a circumferential 'fiang'aa Wall at the other end of said assembly to said flange, a conductor extending between said first terminal and the electrode'on the outer face of said crystal, a second terminal mounted'to said 'secondnamed wall, and "a conductor extend= ing' between" said second terminal and the elec; trade on the inner face of said crystal.-

31A crystal assembly comprising'a pair of cyl= inders; one within the other, forming an annular chamber between, a plate crystal mounted across one end'of the inner cylinder and sealed to the edge thereof, the periphery of said crystal ex tending slightly beyond the'edge of said inner cylinder,- an annular wall sealed to the edge'of said outer cylinder and to the edge-of said crys: tal thereby. to seal said chamber'at' said one end;

a wall at the other end -of 'saldas'sembly sea ed to the cylinder edges to seal said chamber, an insulating fluid in said chamber, and a pair of thin, plate-like electrodes mounted one against each face of said crystal.

4. A crystal assembly comprising a pair of cylinders, one within the other, forming an annular chamber between, a plate crystal mounted across one end of the inner cylinder and sealed to the edge thereof, an annular wall sealed to the edge of said outer cylinder and sealing said chamber at said one end, a wall at the other end of said assemblysealed to the cylinder edges to seal said chamber, said chamber being occupied by an insulating medium, and a pair of thin plate-like electrodes mounted one against each face of said crystal.

5. A crystal assembly comprising a hollow casing having an opening in a face thereof, a plate crystal mounted across the opening and sealed to the edge thereof, a thin electrode mounted against the inner face of said crystal, the edge of said electrode terminating short of the opening in said casing thereby leaving an annulus of bare crystal exposed to the interior of the casing, the interior of said casing being evacuated to increase the arcing resistance across said annulus, a conductor in contact with said electrode, extending thru the evacuated interior of said casing, and penetrating the casing wall, the penetration of said wall being sealed around said conductor to maintain the vacuum, another thin electrode mounted against the outer face of said crystal,

'and a conductor in contact with the other, outer electrode.

6. A crystal assembly comprising a casing having at least one face thereof open, a plate-like crystal mounted to said casing across said open face thereby closing the same, the contacting edges of said crystal and casing being sealed to each other, thin conducting electrodes mounted to both faces of said crystal, a portion of said casing forming a sealed chamber bordered at least by an annulus adjacent the edge of the electrode on the inner face of said crystal, the medium within said chamber being of good insulating properties, whereby to prevent electrical breakdown between said electrodes around the edge of said crystal, and a pair of conductors contacting the electrodes on the respective faces of said crystal.

EARL F. KIERNAN.

REFERENCES CITED UNITED STATES PATENTS Name Date Morgan May 7, 1946 Number 

